With the rapid development of the communications, users have higher requirements for data capacity, which brings higher technical challenges to the communication industry. Confronted with the high requirements, in the next generation wireless network (the fifth generation mobile communication network, 5G), operators consider increasing the data rate for users in the network to a new level, for example, the data capacity of the mobile users per unit area is a thousand times greater than that in 4G network (the fourth generation mobile communication network). A new network architecture called heterogeneous network is proposed in the industry as a key technology that can meet requirements of the operators. In the architecture of heterogeneous network, low-power small base stations (e.g., base stations, relays, and the like of a microcell, a picocell and a femtocell) are deployed and share the same spectral resources with high-power macro base stations (a base station of a macrocell) to achieve the purpose of increasing a spectral efficiency and a data capacity per unit area in the network.
A recent report on energy consumption in a cellular network indicates that up to 82.5% of network energy is consumed on the base station side. That is, in a case that a large number of small base stations are deployed to meet the demand for data capacity of the users, the total energy consumption of the network is multiplied with the increase in the number of base stations in the network. Hence, the energy efficiency problem of the network becomes a research focus of the next generation network. To this end, in the scenario of the heterogeneous network, to improve the energy efficiency of the network, research on the green communication (GR) technology is very important. At present, there are two major international cooperation projects in research on the green communication: the green communication project of the mobile virtual centre of excellence (MVCE) and energy aware radio and network technologies (EARTH). These two cooperative research organizations have invested a lot of manpower and material resources in research on the GR technology.
At present, the research on energy efficiency and spectral efficiency is mainly focused on allocation of resources in the licensed band, while quite a little research is made on the joint use of the unlicensed band and the licensed band. Since additional resources are available on the unlicensed band, licensed assisted access (LAA) technology is proposed so that the cell can operate on both the licensed band and the unlicensed band to achieve the purpose of improving the network capacity by increasing the bandwidth. By jointly using the licensed and unlicensed bands, it is possible to narrow the gap between the limited capacity of the licensed band and the fast-growing rate demand of the users. At present, there are, for example, the following schemes for the joint use of the licensed and unlicensed bands: 1) a scheme in which, for example, a femtocell can access to both a licensed band and an unlicensed band, which mainly takes the usage of the unlicensed band and the coexistence of femtocells and Wi-Fi into consideration; 2) a scheme in which the transmission of small cells on the licensed and unlicensed bands is controlled, which can maximize network throughput while meeting the requirements of quality of service (QoS), but only improves the performance of the network throughput by using interference coordination, without considering the energy efficiency and the spectral efficiency; and 3) a scheme in which energy and spectrum efficiencies are jointly used to optimize an outage capacity, which however only considers resource allocation on the licensed band.